 Now, this is a slide I shared with you, the concept of CT is very attenuation-based. Our focus is to get the best lesion to background contrast, and it's no surprise that we give contrast for almost all oncology indications. Now, for typically at least in the United States, but also the NCCN guidelines suggest for most oncology protocols, IV contrast is must, except if patient has, you know, contrast allergies or renal issues. But oral contrast, they encourage. They don't mend it. They say oral contrast is advised. In our practice, for most oncology application, we use both oral and IV contrast. Every patient gets reformats. Certain patients, we also do image processing using 3D rendering. Now, some of you probably don't use oral contrast. How many of you use oral contrast for oncology protocols? Good number. Great. So, I would say is one thing you keep in mind is sometime we look at an astute radiologist like Aniga or Raju and we think, oh, they don't need any oral contrast. They can do a great job. They have so much experience, but we don't realize our workforce is much younger. A lot of these initial interpretations are done by trainees. They need that confidence of knowing what is normal versus abnormal. So, let's look at this patient. This patient, both patients had right lower quadrant pain, years, someone called. And previous evening, this was a bowel wall thickening. We need colonoscopy. More likely that it's ischemia or tumor, oh, sorry, infection or tumor. This was a young patient. Everyone thought this is lymphoma. There is lymphedinopathy. And, you know, clinically it was not making sense. We repeated study with more oral contrast and you realize this is a pseudo thickening, quite common in secom because of poor mixing of content feces and oral content. Year, it's so easy. There is no question. Same year, we waited for a little longer with oral contrast. That was unapacified bowel loop. Minimizing that false positive is critical because, you know, colonoscopy is a huge expense. In United States, colonoscopy alone is few hundred billion dollar expense. 25% of colonoscopy that CT generates is unindicated. There's nothing. We call bowel wall thickening or something and they find nothing. So, it's so critical that we reduce that expense and also morbidity. You know, detection of certain abnormality. I think, you know, this hypervascular neuroendocrine tumor, carcinoid and bowel will be extremely difficult if the bowel is not distended and we have a good IV contrast. You can see multifocal lesion here. You can appreciate better. This peritoneal metastasis, I'm sure most of us will miss it depending on the day. Without oral contrast, you know, looking at bowel changes, all these requires, you know, good distension of bowel. Some contrast could be neutral or a positive contrast. For post-op situation, I think positive contrast is so desirable. In pelvis, especially looking for peritoneal disease, local recurrence in GYN malignancy, it's so important to have a good bowel of pacification. It makes all the difference in detecting that subtle abnormality. So here, I'm going to show you an example of a rectal cancer which is invading into seminal vesicle. It's so much easier when the rectum is distended. This is a peritoneal implant, which we can miss it. If the bowel is not opacified, you know, when bowel is opacified and you can see those peritoneal implants, you know, the other year, these are obvious but subtle peritoneal disease. Omental changes can be tough if bowel is not opacified. This is one such example where a linear dysplastica, gastric infiltrative gastric cancer can be missed when stomach is not distended. Only way this case was diagnosed with peritoneal disease outside. So having a good bowel opacification, here you can look at the same case. Not easy to interpret, much easy with small bowel loop being opacified. So oral contrast is critical for detecting small pelvic tumor, peritoneal disease or also differentiating normal from abnormal. I want to show you example. This is a post-op case, APR, post-APR, patient was having fever. They wanted to look if there is a leak. This study was done without rectal contrast. And, you know, a resident overnight said that this is an absence, this is a leak. And, you know, I reviewed this study and I said it makes no sense. It's a little defined, corrugated like, you know, margin. This is probably a bowel loop. Let's give some rectal contrast and re-image and you can see what a difference it does. You have a rectal contrast, you're extremely confident that it's not a leak because the plan was to put a catheter, you know, unnecessary. In a post-op setting, you don't want to add more morbidity for the patient. So very easy to make that determination. So if you are in doubt where you are, you know, on the fence with oral contrast, I would say the areas that all the topics that I have put in bold are the ones you should definitely use oral contrast. I think lung, breast cancer, you can ignore it, maybe not. For HCC, prostate cancer, lymphoma, renal tumor, I think it's optional. We are not using oral contrast for these indications. But ovarian cancer, GI tract cancer, pancreatic cancer, bile duct tumor, melanoma, we use oral positive, oral contrast media. Having learned that, I think IV contrast, we all know it's so valuable. But that's not the questionnaire. The question is the timing, your protocol. That dictates how effective will be your staging, how effective will be your diagnosis. Now, I want to share this case of a patient who is high risk for HCC. We scan the patient at 18 seconds from the time of initiation of contrast, then at 25 seconds and at 35 seconds. What you see that at 18 seconds, even though AOTA is enhancing very well, you don't see much in the liver. As you go to 35 seconds, you realize that entire liver is filled with tumor. So if your timing is wrong, your staging is wrong. So knowing that what is the right timing is critical. This is a portal menous phase exam in a patient where we were not suspecting pancreatic cancer. And as you can imagine, there is this hypodense lesion was missed initially. I think we were reviewing the study for something else. This patient had nephrectomy for renal cell carcinoma. The urologist came to me and said, hey, this patient has some nonspecific symptoms. You don't see any recurrence. And I said, I don't see a recurrence. But I see that the pancreatic duct is slightly prominent and there is some heterogeneity in this area. I'm worried this patient has a pancreatic cancer. So this patient was diagnosed with unsuspected pancreatic cancer. The patient had a resection, negative margin, no metastases and did well for almost seven years after resection. But this could have been missed. The timing of contrast is so critical. The point I want to make is knowing the clinical indication and using the right protocol is essential for you to be more effective in care delivery. So this case, understandable, we were not suspecting pancreatic cancer. So to understand protocol, let's look at these contrast enhancement curve. I won't bore you with a lot of discussion on this. What I want to tell you is on the X and Y axis, you can have the time, you have enhancement and these are the curves. So if you start here at zero, at certain time, pulmonary arteries will enhance first, followed by aeoda. Then you will see a liver will enhance much later and then we will see the portal venous phase and this is for arteries for runoff. These curves tells you what, based on the clinical indication, what your timing should be for arterial phase acquisition. Why did I say arterial phase acquisition? Because portal venous phase is much longer. It's the arterial phase where the window is much narrow. Getting the right time in liver, for example, as I said, 35 seconds, somewhere between 35 to 40 seconds is the better window. If you scan earlier, you will get an angiogram, but it won't be a great image for hepatic arterial dominant phase. These curves, just to show you, like if you're looking at aeoda, what should be the timing if you're doing empiric delay for liver, what should be your timing, how much additional seconds you need to add to get the right timing. And again, timing matters mainly for arterial phase because the window of opportunity is narrow there. For portal venous phase, you will not get wrong. You have almost more than a one-minute window for portal venous phase. As you can see, portal venous phase is much longer and delayed phase, whether you are at 3 minutes, 5 minutes, no one cares. So it's mainly the arterial phase. As long as you remember that part, that's great. The good news is we don't have to memorize these things. We can pre-program using these power injectors, which has a great operating system. You can pre-program all your protocols. So if it is pancreas protocol, the technologist can use that. The power injector will deliver that much dose of contrast at a rate and the scanner can synchronize when we need to scan. I know this is a busy slide. I'm going to give you some time to understand how the protocols are important. The timing for acquisition is important. So let's look at it. When we are looking at angiograms or hypervascular lesion in pancreas, we scan a little bit earlier anywhere from 20 to 30 seconds from the time of start of injection. For liver, the contrast arrives in liver about 10 to 15 seconds later. So the timing is 30 to 40 seconds for liver lesion, hypervascular liver lesions. For pancreas, what you're trying to do is for pancreatic adenocarcinomas, you want to maximize pancreatic enhancement. Pancreatic cancer tends to be hypodense. So in the pancreatic phase, the arteries, the veins are well opacified and the tumor just stands out. And portal venous phase, I won't spend time that's much easier. Delayed phase is not a big deal when we need excretory phase. Again, you have a great window and certain indication. One can do, especially for bladder cancer, you can do 10 to 15 minutes delay. Now, one additional point I want to share with you is we rely heavily on the arterial phase for detection, but we also need to look at the venous phase. So for example, HCC, the diagnostic criteria doesn't rely on arterial phase only. Washout is equally important because you can imagine there are many benign lesion, you know, adenomas, FNHs, shunts, they will all light up in arterial phase. And they can occur in chronic liver disease patients, but they won't washout. So washout is important. What does washout means? If the lesion that is enhancing more than background, that is called arterial phase enhancement. If the lesion turns darker than background, that is considered washout. So that defect is important because every lesion will de-enhance. So they will be lighter than arterial phase, but washout means defect and that's the ominous sign. More than the arterial phase, it's the washout which has more than 90% specificity and that is linked to angiogenesis, the leakiness of the vessel. In large patients, and as we know, there are a lot of cancer patients who are obese, especially pancreatic cancer, it is prudent because of the higher blood volume you add about 20 cc's more contrast and add additional 5 second delay to compensate for higher blood volume. So that's a simple message I want to give you. It's just a little bit more contrast, takes you a long way and some delay, extra delay helps you with better image quality.